**Core Concept**
The equilibrium potential for a particular ion is the electrical potential at which the concentration gradient for that ion is balanced by the electrical gradient, resulting in no net movement of the ion across the cell membrane. This concept is crucial in understanding how ions distribute across cell membranes and how it affects cellular functions.

**Why the Correct Answer is Right**
The equilibrium potential for Cl- (ECl) can be calculated using the Nernst equation: ECl = (RT/F) * ln([Cl-]outside / [Cl-]inside), where R is the gas constant, T is the temperature in Kelvin, F is the Faraday constant, and [Cl-] is the concentration of Cl- in moles per liter. Given that the concentrations of Cl- inside and outside the cell are 8 mmol/L and 120 mmol/L, respectively, and the temperature is 37°C (310 K), we can plug in the values to calculate ECl.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is not provided.
* **Option B:** This option is not provided.
* **Option C:** This option is not provided.

**Clinical Pearl / High-Yield Fact**
The Nernst equation can be used to calculate the equilibrium potential for any ion, but it's essential to remember that the actual membrane potential may not be equal to the equilibrium potential due to various factors like ion channels, pumps, and electrotonic potentials.

**Correct Answer:** C. -77 mV.